As wireless communication systems such as cellular telephone, satellite, and microwave communication systems become widely deployed and continue to attract a growing number of users, there is a pressing need to accommodate a large and variable number of communication subsystems transmitting a growing volume of data with a fixed resource such as a fixed channel bandwidth accommodating a fixed data packet size. Traditional communication system designs employing a fixed resource (e.g., a fixed data rate for each user) have become challenged to provide high, but flexible, data transmission rates in view of the rapidly growing customer base.
The third generation partnership project long term evolution (“3GPP LTE”) is the name generally used to describe an ongoing effort across the industry to improve the universal mobile telecommunications system (“UMTS”) for mobile communications.
Recently, extensions of the 3GPP standards include the support for UEs and NBs performing high speed packet access (HSPA). High speed packet access communications are particularly appropriate for bursty, date intensive service applications. For example, voice over internet protocol (VoIP) and video broadcasting to and from mobile devices over an air interface are very bursty in nature. The addition of HSPA capability is expected to provide mobile users with a broadband experience that is similar to, or even supplants and replaces, a wired broadband connection, and is particularly useful for video download/upload, audio download/upload, VoIP, internet browsing, and transmission of large data files and/or audio or video streams in a time sensitive manner. VoIP service in particular places high demand on the system as the transmission of digitized voice signals must occur quickly enough, and the system must be responsive enough, to avoid the voice users ever experiencing noise or delay in the voice communications that is caused by waits in the system.
In wideband CDMA (WCDMA) based systems HSPA provides high speed downlink packet access (HSDPA) and high speed uplink packet access (HSUPA). Further, as the need for additional performance in mobile systems including the UMTS terrestrial radio access network (UTRAN) and the more advanced evolved UTRAN (E-UTRAN) systems continues, improvements referred to as evolved HSPA are being defined. One improvement to further increase performance in HSPA enabled systems is the use of dual cell or sometimes dual carrier HSPA (DC_HSPA). By using additional carriers or cells to carry data to and from a communications terminal at high speed, additional capacity for data throughput is made available.
The improvements are being made to cope with continuing new requirements and the growing base of users, and higher data rates and higher system capacity requirements. Goals of this broadly based project include improving communication efficiency, lowering costs, improving services, making use of new spectrum opportunities, and achieving better integration with other open standards and backwards compatibility with some existing infrastructure that is compliant with earlier standards.
The wireless communication systems as described herein are applicable to, for instance, UTRAN and E-UTRAN compatible wireless communication systems and WCDMA systems that support HSPA.
In the UTRAN architecture, radio network subsystems (RNS) are divided into portions including the radio network controller (RNC) and several base stations (referred to as a Node B or enhanced Node B (eNB) in the 3GPP specifications). Mobile communication terminals such as cell phones are referred to as user equipments (UEs). Each Node B/eNB may be in radio contact with multiple UEs (generally, user equipment including mobile transceivers or cellphones, although other devices such as fixed cellular phones, mobile web browsers, laptops, PDAs, MP3 players, and gaming devices with transceivers may also be UEs) via the radio Uu interface.
In the UTRAN architecture, a core network (referred to as CN) may be connected to any one of several external networks, or more than one, including networks such as the Public Switched Telephone Network (PTSN), the Integrated Services Digital Network (ISDN) and, of course, the Internet.
There are several different connections between the network elements that make up the telecommunications system. An Iu interface connects the CN to the UTRAN elements. An interface referred to as LUR connects Node Bs. A radio network layer (RNL) protocol is provided for signaling on the LUR interface and is referred to as the radio network subsystem application part (RNSAP). An RNC is connected to a Node B by an interface referred to as Iu. The Iu interface allows communications of required radio resources to the Node B from the RNC. This interface is then used by the RNC to configure the network and allocate resources such as cells controlled by a Node B, and to configure channels for communications to the UEs.
Importantly, one Node B or eNB can serve multiple cells. A UE is connected to a Node B through an interface referred to as the Uu interface. The UE has a subscriber identity module (USIM) and mobile equipment (ME). The ME includes the radio transceiver, and the hardware and software functions that are used by the user to make calls, send messages, transmit video and photographs, send email, browse the web and so forth on the mobile device.
In the present discussion, particular attention is paid to the HSPA. The HSPA includes HSDPA and HSUPA for downlink and uplink transmissions. The HSDPA has several dedicated channels, including the HS-DCH (high speed downlink channel) which is further divided into the HS-DPCH, the high speed dedicated physical channel and the HS-DCCH, the high speed dedicated control channels, which are present in both the downlink and the uplink. A shared channel, the high speed downlink shared channel (HS-DSCH) may be mapped on a high speed physical downlink shared channel (HS-PDSCH) or more than one in the physical layer.
The lowest layer of communication in the UTRAN or e-UTRAN system, Layer 1, is implemented by the Physical Layer (“PHY”) in the UE and in the Node B or e-Node B. The PHY performs the physical transport of the packets between them on an over the air interface using radio frequency signals. In order to ensure a transmitted packet was received, an automatic retransmit request (“ARQ”) and a hybrid automatic retransmit request (“HARQ”) approach is provided. Thus, whenever the UE receives packets through one of several downlink channels, including dedicated channels and shared channels, the UE performs a communications error check on the received packets, typically a Cyclic Redundancy Check (“CRC”), and in a later subframe following the reception of the packets, transmits a response on the uplink to the e-Node B or base station. The response is either an Acknowledge (“ACK”) or a Not Acknowledged (“NACK”) message. If the response is a NACK, the e-Node B automatically retransmits the packets in a later subframe on the downlink (“DL”). In the same manner, any uplink (“UL”) transmission from the UE to the e-Node B is responded to, at a specific subframe later in time, by a NACK/ACK message on the DL channel to complete the HARQ. In this manner, the packet communications system remains robust with a low latency time and fast turnaround time.
The use of HSPA in the downlink (HSDPA), from the NB or eNB to the UE, is fairly well understood by the existing or proposed standard documents. The support for HDSPA is provided by defined and agreed standard transport channels. The HS-DSCH is defined and supports adaptive coding and modulation. A scheduler function is provided at the Node B level that provides dynamic resource allocations. Signaling is provided to users on the downlink control channel, the High Speed Signaling Control Channel (HS-SCCH); including information such as UE identity, using a UE specific field including cyclic redundancy check (CRC) for addressing a specific UE on the shared channel, fields such as the Transport Format and Resource Indicators (TRFI) for identifying a scheduled resource and a transmission format, and support for hybrid automatic retransmission requests (HARQ). As defined, each UE using the HSDPA downlink may monitor up to four HS-SCCH channels. An uplink transport is defined for the UE to send uplink traffic, the High Speed Dedicated Physical Control Channel (HS-DPCCH) which allows transmission of channel quality information (CQI) and ACK/NACK information for HARQ support. For example, reference is made to the document provided by the 3GPP standards setting organization at www.3gpp.org entitled “Media Access Control (MAC) Protocol Specification; Release 8.5.0”, numbered Technical Specification 25.321, which document is herein incorporated by reference.
For high speed uplink packet access (HSUPA), sometimes referred to as Enhanced Uplink (EUL), a different scheme is defined. The channel definitions are different because the uplink transmissions use non-orthogonal signal transmission. Transport channels are referred to as Enhanced Dedicated Channels (E-DCH). An important aspect for uplink transmissions on dedicated channels on shared radio resources is the UE power control needed to address the near-far transmitter problems, so that UEs physically near the receiving NB do not “stomp out” uplink traffic from remotely located UEs. In addition, UE handoff is supported including “soft” or “softer” handoffs. In UE handoffs, the UE may be transmitting to more than one receiving NB or eNB. Thus, the radio network controller (RNC) may be configured to put together these disparate uplink packet messages in the correct order. Packets may be received by differing NBs, and packets may be received in duplicate form due to the handoff procedure. Thus, the RNC may be configured to reorder and restore the original sequence of packets.
Additional channels have been defined for the HS uplink, including the enhanced dedicated physical data channel, or E-DPDCH, for dedicated uplink data transmission. This channel transports packets including scheduling information, buffer status and the like. The enhanced dedicated physical control channel, E-DPCCH, provides control information for decoding and detecting the E-DPDCH channel. Also, some information may be provided to inform the resource scheduler if the UE has resources (e.g., sufficient uplink data for transmission ready in the UE data buffers) for transmission. Additional handshake or control channels include the enhanced HARQ Acknowledgement Indicator Channel (E-HICH) for transmitting HARQ signals such as ACK/NACK signals to the sender. Some channels are defined for resource allocation to the UE, the enhanced relative grant channel (E-RGCH) and the enhanced absolute grant channel (E-AGCH) which provide a transport channel to enable the eNB to allocate resources to one, or one of several, UEs.
Because the HARQ protocol requires support of out of order delivery of the ACK/NACK responses, a reordering function is required in higher layer protocols. Thus, a separate higher layer service is defined, at the MAC level, called MAC-es/MAC-is. This layer is located at the RNC because the UE may be in soft and softer handover and thus, the packets on the uplink transport channel may be received by different eNBs or NBs. Some packets may be repeated or lost as the UE transmits during the handoff, and the RNC may be able to recover those packets using CRC and error detection and correction techniques on the reordered packets.
Additional features have been defined for the high speed packet access communications. The concept of dual cell or dual carrier HSPA (DC-HSPA) extends the performance of HSPA. In DC-HSPA, two carriers are used to communicate high speed packets to and from UEs by an eNB. This capability is particularly useful as the signal carriers are often assigned in 10-15 Mhz spectrum pairs, so by using both pairs, additional system performance is attained using already allocated bandwidth. In the downlink case, the DC-HSDPA protocols have been defined, including a primary or anchor carrier and a secondary carrier connected to two UEs from a single eNB, or alternatively, two carriers connected to a single UE. By using advanced load carrying, the capacity of the transport channels may be increased over the use of single carrier HSDPA. For the DC-HSDPA, the relationships between the primary carrier and the secondary carrier are such that the receiver (UE) can locate one carrier and then, without the necessity of doing a blind search, set its receiver filtering properly to receive the second carrier.
For the uplink case (transmissions from one or two UEs to a NB over the dual carriers), the use of dual carriers is presently contemplated, but the signaling considerations are different. Requiring support for handoff of the UE from one NB to another means that the packets communicated on the uplink transport facility from the UE may be received at more than one NB. Thus, a higher level layer must perform a reordering. Further, the secondary carrier may not be easy to locate. The need for determining the secondary carrier receiver information is also complicated. Unlike the downlink case, the location or time parameters of the secondary carrier may not be known or easily determinable from the primary carrier properties. The NB could perform a blind search for the carriers but this approach, while feasible, would impose unacceptable burdens on the system and reduce performance, thus undoing gains that are sought by the use of the dual carrier scheme.
A need thus exists for systems and methods to efficiently provide the signaling needed to support the DC-HSUPA capability for UEs and NBs in an over the air interface radio frequency communications system, with efficient approaches provided to eliminate or reduce the need for blind searches and to prevent errors, and without the disadvantages of the known prior approaches.